Minimally invasive medical techniques have been used to reduce the amount of extraneous tissue which may be damaged during diagnostic or surgical procedures, thereby reducing patient recovery time, discomfort, and deleterious side effects. Traditional forms of minimally invasive surgery include endoscopy. One of the more common forms of endoscopy is laparoscopy, which is minimally invasive inspection or surgery within the abdominal cavity. In traditional laparoscopic surgery, a patient's abdominal cavity is insufflated with gas and cannula sleeves are passed through small (approximately 1¼ cm.) incisions in the musculature of the patient's abdomen to provide entry ports through which laparoscopic surgical instruments can be passed in a sealed fashion.
The laparoscopic surgical instruments generally include a laparoscope for viewing the surgical field and working tools defining end effectors. Typical surgical end effectors include clamps, graspers, scissors, staplers, and needle holders, for example. The working tools are similar to those used in conventional (open) surgery, except that the working end or end effector of each tool is separated from its handle by an approximately 30 cm. long extension tube, for example, so as to permit the operator to introduce the end effector to the surgical site and to control movement of the end effector relative to the surgical site from outside a patient's body.
In order to provide improved control of the working tools, it may be desirable to control the instrument with teleoperated actuators. The surgeon may operate controls on a console to indirectly manipulate the instrument that is connected to the teleoperated actuators. The instrument is detachably coupled to the teleoperated actuators so that the instrument can be separately sterilized and selected for use as needed instrument for the surgical procedure to be performed. The instrument may be changed during the course of a surgery.
Performing surgery with teleoperated actuated instruments creates new challenges. One such challenge is providing a teleoperated motor mechanism that supports the teleoperated actuated surgical instruments that can be positioned with respect to the patient. These mechanisms are fairly heavy, weighing perhaps twelve to twenty-four kilograms. The mechanisms must be moved over a patient and positioned carefully. Therefore it is necessary to counterbalance the surgical instrument, the related actuators, and the support structure so that the surgical instrument can safely and easily be positioned. Counterbalancing is made more difficult because the various surgical instruments may have various weights.
It would be desirable to provide a way of counterbalancing a surgical instrument, its related actuators, and support structure that is effective with changeable surgical instruments of various weights.